Hi,
John Cole of Pearland, Texas, has been doing some very productive research
in improving and finding cheap ways to construct a Lehman.  He has been
using two Lehman sensors (side by side) with a N - S orientation to check
out the results of using various coil sizes.  He has a coil winding machine
and has wound and used coils with 6,000 to 16,000 turns. He has found, for
example, that a 14,000 turn coil will give approximately 20% better results
than a 12,000 turn using the same size wire.  (The two giant surplus magnets
used with his two Lehman sensors have approximately the same magnetic flux
density.)

He has discovered that Radio Shack speaker magnets (one mounted above the
other in a wooden framework and not connected in any way) are just as
effective as the giant war surplus magnets he has been using.  The giant
magnets are extremely hard to find but the RS magnets are plentiful, cheap,
and often can be obtained free in discarded bad speakers. He has even broken
a single magnet into two pieces and used the two parts to effectively detect
earthquakes.

John discovered a method of easily increasing the period of the Lehman
pendulum up to 16 seconds or so by decreasing the friction at the pivot
point.  He did this well over a year ago by using a ball bearing at the
pivot point. (The period of my Lehman was increased from 12 sec to 16
seconds using John's method.) I have noticed that several other amateur
seismologists recently have switched to John's method. John has been
detecting earthquakes that none of the Texas stations have been reporting
via PSN "event" (except for the Corpus Christi station).  You have not heard
from John because he has been using two Angus-Esterline chart recorders in
conjunction with his two Lehman detectors.  This should change soon,
however, as John is now using Larry's a/d card and amp and hopefully will
begin uploading quakes to PSN "event"  within a few weeks.  My hat is off to
John because of his productive research.  You can see some of the results on
his SEISMOLOGY IN PEARLAND, TEXAS web page at:
http://freeweb.pdq.net/fxc/four.html

I congratulate science teachers Don Wheeler and Pat Schneider of Carroll
High School in Monroe, Louisiana.  Don and Pat recently visited John and me
to study our seismograph stations.  They returned to Monroe and obtained
funding to construct a seismograph station at Carroll HS in Monroe. I do not
think it will be long before you will see their seismograms on PSN "event."
You can see their picture on my SEISMOLOGY IN FRIENDSWOOD, TEXAS web page at
http://freeweb.pdq.net/fxc/

Frank Cooper, Friendswood, Texas.





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